The presently disclosed embodiments relate generally to layers that are useful in imaging apparatus members and components, for use in electrostatographic, including digital, apparatuses. More particularly, the embodiments pertain to an improved electrostatographic imaging member incorporating specific anti-oxidants into the charge transport layer to achieve substantially reduced lateral charge migration (LCM).
Electrophotographic imaging members, e.g., photoreceptors, photoconductors, and the like, include a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the substantial absence of light so that electric charges are retained on its surface. Upon exposure to light, charge is generated by the photoactive pigment, and under applied field charge moves through the photoreceptor and the charge is dissipated.
In electrophotography, also known as xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. Charge generated by the photoactive pigment moves under the force of the applied field. The movement of the charge through the photoreceptor selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image. This electrostatic latent image may then be developed to form a visible image by depositing oppositely charged particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
Multilayered photoreceptors or imaging members have at least two layers, and may include a substrate, a conductive layer, an optional undercoat layer (sometimes referred to as a “charge blocking layer” or “hole blocking layer”), an optional adhesive layer, a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, and an optional overcoating layer in either a flexible belt form or a rigid drum configuration. In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provides better photoreceptor performance. Multilayered flexible photoreceptor members may include an anti-curl layer on the backside of the substrate, opposite to the side of the electrically active layers, to render the desired photoreceptor flatness.
The charging of the photoreceptor is necessary for the proper operation of an electrostatographic apparatus. However, in normal operations of the photoreceptor, by-products are formed which can interact with the surrounding atmosphere and with the photoreceptor itself to produce substantial negative effects on the photoreceptor and the resulting copy. For example, exposure to corona effluents during xerographic cycling induces unwanted surface conductivity on the photoreceptor. The increase in surface conductivity manifests itself as a reduction in print quality. These are sometimes called lateral charge migration (LCM) and/or deletion. This effects can cause the output of a printed copy to appear blurry or have areas where the image is entirely missing (e.g., deleted). Such line spreading and/or washout occur as charges become mobile on the surface of the photoreceptor. If extended exposure occurs the washout can become severe enough to completely delete the affected print area.
As there is a demand for photoreceptors capable of working at higher speeds, charge transport molecules such as high quality N,N,N,′N′-tetra(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine- are added to the charge transport layer to impart higher discharge rates. Unfortunately, charge transport layers having high quality N,N,N,′N′-tetra(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine have high sensitivity to corona-induced LCM. Thus, there is a need for way to avoid LCM problems that appear in the above-described imaging devices.
Conventional photoreceptors are disclosed in the following patents, a number of which describe the presence of light scattering particles in the undercoat layers: Yu, U.S. Pat. No. 5,660,961; Yu, U.S. Pat. No. 5,215,839; and Katayama et al., U.S. Pat. No. 5,958,638. The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrostatographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule.”
Additional conventional photoreceptors and their materials are disclosed in, for example, U.S. Pat. Nos. 5,489,496, 4,579,801, 4,518,669, 4,775,605, 5,656,407, 5,641,599, 5,344,734, 5,721,080, 5,017,449, 6,200,716, 6,180,309, and 6,207,334, the disclosures of each of which are totally incorporated herein by reference. U.S. Pat. No. 7,267,917 (Tong et al.), the disclosure of which is totally incorporated herein by reference, discloses a charge transport layer composition for a photoreceptor including at least a binder, at least one arylamine charge transport material, e.g., N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine, and at least one polymer containing carboxylic acid groups or groups capable of forming carboxylic acid groups. The charge transport layer forms a layer of photoreceptor, which also includes an optional anti-curl layer, a substrate, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, and optionally one or more overcoat or protective layers.
As used herein, “discharge rate” refers to the voltage drop over time and is based upon a discharge over a discharge interval at a given light intensity, wherein discharge is defined as the voltage drop or difference between the initial surface voltage before light exposure and the surface voltage after light exposure at the end of the discharge interval. Discharge interval is defined as the time period from the light exposure stage to the development stage (which is essentially the time available for the photoreceptor surface to discharge from an initial voltage to a development voltage) and light intensity is defined as the intensity of light used to generate discharge in the photoreceptor. The exposure light intensity influences the amount of discharge, and increasing or decreasing light intensity will respectively increase or decrease the voltage drop over a given discharge interval.